@Gavinx: I had exactly the same need, and found a way to solve it. The solution was to make my own 'Map style'. (One of the nice properties of OsmAnd is that the map styles are defined in xml files, and we can modify the existing ones and/or add new ones without changing the OsmAnd software itself). I you want, I can attach/send the style that I made, after I have reviewed it and cleaned it a bit first. When installed (i.e., xml file copied to the rendering folder), the new map style appeares in the menu in OsmAnd, and I can select it just like any other map style (OsmAnd, Touring view, UniRS, LightRS,..., MyNewStyle) in the menu when running OsmAnd.
-Gunnar